Preparation

With a small knife trim a strip down the length of the rounded side of each celery rib to form a flat bottom and cut the ribs on the diagonal into 1 1/2-inch boats. Put the celery boats in a bowl of ice and cold water and chill them, covered, until ready to assemble the hors d'oeuvres. Cut 6 ounces of the Gruyère into 1-inch julienne strips and grate fine the remaining 2 ounces. In a food processor or blender combine the grated Gruyère and the pine nuts and blend the mixture unitl it is a paste. With the motor running add the oil in a stream and blend the pesto until it is emulsified. In a bowl toss the julienne Gruyère with the pesto and fill the celery boats, drained and patted dry, with the mixture. The hors d'oeuvres may be made up to 1 day in advance and kept covered and chilled. Serve the hors d'oeuvres at room temperature.